What is the difference between synchronized and unsynchronized in java

Packages in Java. Flow Control in Java. Loops in Java. Jump Statements in Java. Arrays in Java. Strings in Java. OOPS in Java. Constructors in Java. Interfaces in Java. Keywords in Java. Exception Handling in Java. Collection Framework. Multi-threading in Java. Thread 1 continues and now is printing out an empty list not what it wanted to do. Labels: Java. Unknown March 18, at PM. Gov July 3, at AM. At the start, on CHM only one segment is created and then dynamically other segments are created using ensureSegments method.

ConcurrentHashMap internally maintains an array of Segments. I think one explanation that you need to add is that use ConcurrentHashMap. It allows concurrent modification of the Map from several threads without the need to block them. Use the second option if you need to ensure data consistency, and each thread needs to have an up-to-date view of the map.

Use the first if performance is critical, and each thread only inserts data to the map, with reads happening less frequently. Post a Comment. Synchronized vs Concurrent Collections Though both Synchronized and Concurrent Collection classes provide thread-safety, the differences between them come in performance , scalability, and how they achieve thread-safety.

The main reason for this slowness is locking; synchronized collections lock the whole collection e. They achieve thread safety by using advanced and sophisticated techniques like lock stripping. For example, the ConcurrentHashMap divides the whole map into several segments and locks only the relevant segments, which allows multiple threads to access other segments of the same ConcurrentHashMap without locking.

Similarly, CopyOnWriteArrayList allows multiple reader threads to read without synchronization and when a write happens it copies the whole ArrayList and swaps with a newer one.

So if you use concurrent collection classes in their favorable conditions like for more reading and fewer updates, they are much more scalable than synchronized collections. It's my personal experience where I have improved performance by using ArrayList where legacy codes are unnecessarily used Vector etc.

JDK 1. And, If you are new to the Java world then I also recommend you go through these Java Collections Courses from Pluralsight and Udemy to learn Java in a better and more structured way. This is one of the best and up-to-date courses to learn Java online. Many concurrent applications will benefit from their use. So what is the difference between Hashtable and ConcurrentHashMap , both can be used in a multi-threaded environment but once the size of Hashtable becomes considerably large performance degrades because for iteration it has to be locked for a longer duration?

That's all about the difference between synchronized and concurrent collection classes in Java. In Summary, concurrent collections use advanced techniques to achieve thread-safety without compromising Scalability.

For example, ConcurrentHashMap only locks a certain portion of Map while Hashtable locks a full map while doing iteration or performing any write operation. Share to Twitter Share to Facebook. Labels: collections interview questions , core java , core java interview question , java collection tutorial. What is the difference between synchronized and non-synchronized collection classes in Java?

Ask Question. Asked 7 years, 9 months ago. Active 1 year, 9 months ago. Viewed 34k times. I was reading about Java's collections and then I read this line: "None of the collection classes are synchronized, but as you will see later in this chapter, it is possible to obtain synchronized versions. Improve this question. Michael Incredible Incredible 1 1 gold badge 4 4 silver badges 16 16 bronze badges. The synchronized ones are, err, synchronized. There is no such thing as 'ASynchronized'.

Solution: stackoverflow. Add a comment. Active Oldest Votes. Improve this answer. Gupta A.